Relay panels, chassis for electrical equipment, and a variety of other complicated electrical devices must be tested to confirm that the relays function properly and that other electrical properties such as continuity and insulation are proper. Special problems can be encountered in connection with the testing of relays for open circuits and short circuits. To test for proper relay operation, an external power supply must be connected to the relay coil, and resistance measurements or other measurements of the relay contacts must be taken to confirm that the contacts open and close properly.
The traditional approach to relay testing makes use of an external energization matrix to actuate the relay. An interface cable extending from the test equipment to the unit under test must be split into two branches in order to provide the necessary connections to the test point matrix and the external energization matrix. Because of the need for a split cable, the interface cable must be specially constructed in a manner making it useful only for one particular product. The need for a different special cable for each product leads to excessive cable requirements and high overall cable costs. If a product has a design change involving moving or adding relays, a new interface cable is required. This further complicates the cable requirements and aggravates the cost problem. All of these problems are increased when the number of relays in the product increases.